A great challenge in wireless telecommunications is to provide spatial allocation of radiation power associated with radio transmission from base stations in directions where information transfer capacity is required and to reduce radio transmission from directions where no radio transmission is needed or the radio transmission may be non-beneficial. Spatial allocation involves directing radiation patterns in desired directions and controlling characteristics, such as shape, of the radiation patterns. Spatial allocation is usually enabled by controllable radiation patterns, which are typically provided by antenna arrays that comprise a plurality of independent antenna units.
Several mechanical means for controlling the characteristics of a radiation pattern provided by antenna arrays can be considered. The antenna arrays may be equipped with parasitic patches in the front or in the sides of patch elements or the shape of reflector in the antenna arrays may be changed. In these solutions, however, large mechanical movements of antenna parts are needed to control the characteristics of the radiation pattern. Furthermore, the impedance and/or the bandwidth of the antenna units may change as a result of changing the physical characteristics of the antenna arrays.
Therefore, it is useful to consider other techniques for controlling the characteristics of radiation patterns provided by an antenna array.